Asynchronous scanning display projection

Abstract

A scanning projector includes a mirror that scans in two dimensions, at least one of which is sinusoidal. A digital phase lock loop locks to the sinusoidal movement of the mirror. A free-running pixel clock is provided. An interpolation component interpolates pixel intensity data from adjacent pixels based on the position of the mirror when a pixel clock arrives.

What is claimed is: 
     
       1. An apparatus comprising:
 a scanning mirror that moves in at least one dimension, the scanning mirror including at least one position sensor to sense a position of the scanning mirror and to provide a position signal; 
 a loop circuit coupled to receive the position signal and to generate a phase signal locked to the position signal, the loop circuit being clocked by a pixel clock that is asynchronous with respect to vertical and horizontal sweeps of the scanning mirror; 
 a free-running oscillator to generate the pixel clock that is asynchronous with respect to vertical and horizontal sweeps of the scanning mirror; and 
 an interpolation component responsive to the pixel clock and the phase signal, the interpolation component to interpolate between pixels based on the phase signal at times specified by the pixel clock. 
 
     
     
       2. The apparatus of  claim 1  wherein the scanning mirror moves sinusoidally in the at least one dimension. 
     
     
       3. The apparatus of  claim 2  wherein the scanning mirror moves linearly in a second dimension. 
     
     
       4. The apparatus of  claim 2  wherein the scanning mirror moves sinusoidally in a second dimension. 
     
     
       5. The apparatus of  claim 1  wherein the scanning mirror moves in two dimensions, and the interpolation component interpolates between pixels in both dimensions. 
     
     
       6. The apparatus of  claim 1  wherein the loop circuit includes a component to produce a sine of the phase signal, and the interpolation component is responsive to the sine of the phase signal. 
     
     
       7. The apparatus of  claim 1  wherein the position signal is a horizontal sync signal. 
     
     
       8. The apparatus of  claim 1  wherein the free-running oscillator comprises a crystal oscillator. 
     
     
       9. The apparatus of  claim 1  wherein the scanning mirror moves in two dimensions, and the interpolation component interpolates between pixels in one of the two dimensions. 
     
     
       10. The apparatus of  claim 1  further comprising a laser light source to produce laser light to reflect off the scanning mirror. 
     
     
       11. A mobile device comprising:
 at least one laser light source; 
 a scanning mirror to reflect light from the at least one laser light source; 
 a position sensor to detect a position of the scanning mirror and to produce a position signal; 
 a phase locked loop circuit to produce a phase signal locked to the position signal, wherein the phase locked loop circuit is clocked by a pixel clock that is asynchronous with respect to vertical and horizontal sweeps of the scanning mirror; 
 a free-running oscillator to provide the pixel clock that is asynchronous with respect to vertical and horizontal sweeps of the scanning mirror; 
 a frame buffer to hold pixel data; and 
 an interpolation component coupled to receive pixel data from the frame buffer, the interpolation component responsive to the phase signal to produce a commanded luminance at times specified by the pixel clock. 
 
     
     
       12. The mobile device of  claim 11  wherein the mobile device comprises a cellular telephone. 
     
     
       13. The mobile device of  claim 11  further comprising a video input port to receive an image from which the pixel data is determined. 
     
     
       14. The mobile device of  claim 11  wherein the scanning mirror comprises a microelectromechanical system (MEMS) device. 
     
     
       15. The mobile device of  claim 11  wherein the scanning mirror oscillates sinusoidally and the phase signal is a linearly increasing phase value that represents a current position of the scanning mirror. 
     
     
       16. The mobile device of  claim 11  wherein the interpolation component interpolates pixel data in two dimensions. 
     
     
       17. A method of projecting an image using a raster scanning projector with a free-running pixel clock comprising:
 sensing a position of a scanning mirror and generating a position signal that reflects the position of the scanning mirror; 
 generating the free-running pixel clock with a free-running oscillator such that the free-running pixel clock is asynchronous with respect to the position signal; 
 phase locking a phase signal to the position signal using a phase locked loop that is clocked using the free-running pixel clock; and 
 interpolating pixel data based on the phase signal at times specified by the free-running pixel clock. 
 
     
     
       18. The method of  claim 17  wherein generating a position signal comprises generating a horizontal sync signal. 
     
     
       19. The method of  claim 18  wherein phase locking a phase signal to the position signal comprises:
 creating a sync signal from the phase signal; 
 comparing the sync signal and the position signal; and 
 modifying a phase of the phase signal. 
 
     
     
       20. The method of  claim 17  wherein interpolating comprises interpolating based on a sine of the phase signal.